The compound 1,3-diamino-4,6-dinitrobenzene (“DADNB”), which is represented by the structure of the following Formula (I):
is conventionally used as a starting material or intermediate in the preparation of a variety of products, which include dyes, pharmaceuticals, and monomers for incorporation into polybenzimidazole polymers such as those described in U.S. Pat. No. 3,783,137.
DADNB can be made by contacting a suspension of 1,3-dichloro-4,6-dinitrobenzene (“DCDNB”) in glycol with ammonia and heating, according, for example, to the method described in Boyer et al, J. Am. Chem. Soc., 82, 2213 (1960). Current processes for making DADNB produce a by-product glycol ether, as represented by the structure of the following Formula (II):

DADNB is very difficult and costly to recrystallize because of its poor solubility in common solvents, and this glycol ether impurity thus remains in the final DADNB product. As a consequence, the purity and properties of downstream products made directly or remotely from DADNB, such as 1,2,4,5-tetraminobenzene (“TAB”), is compromised.
For example, TAB is a precursor to high-performance polymers such as polybenzimidazoles, which are used to make high-performance, high-strength fibers. The purity of the precursors affects the polymer molecular weight that can be achieved, which in turn determines whether satisfactory fibers can be produced.
There thus remains a need for an improved process for making high-purity 1,3-diamino-4,6-dinitrobenzene.